This collaborative project will investigate a staphylococcal protein, the toxic shock syndrome exoprotein (TSSE) that plays a key role in the etiology of TSS. The protein will be analyzed from two points of view: (1) as a representative of a larger class of variable bacterial traits that involve accessory proteins, many of which are involved in pathogenicity and (2) as the prototype of a bacterial factor that is involved in disease but is not itself a toxin. In the first part, the structure of the variable genetic element carrying the TSSE determinant will be analyzed and the possibility that it is a transposon will be investigated. In the second part, an attempt will be made to identify domains of the protein associated with its various biological activities: reticulo-endothelial blockade; T-lymphocyte mitogenicity, pyrogenicity, immunosuppression.